The invention relates to a display apparatus for tape running positions used in tape recorders, for example.
In general, the tape recorder is provided with a counter for indicating or displaying tape running positions or an amount of tape running. Frequently, for the tape counter a mechanical tape counter is used in which a numeral corresponding to the rotational speed of a tape reel is displayed by a mechanical means. The mechanical tape counter, however, suffers from various inherent factors causing errors and is insufficient in display precision for the tape running position. One of the countermeasures against the disadvantage is a recent development of an electronic counter for displaying the tape running position by means of an electronic means. By convention, the electronic tape counter forms a signal representing the tape running position from a predetermined correlation between the rotational speeds of the capstan shaft and the take-up (or supply) reel shaft in the tape transport system. In such an electronic counter, the tape is not driven in a fast forward wind or rewind mode, so that the correlation between the capstan and reel shafts is independent of the tape running position. For this, the conventional electronic tape counter loses the function of a tape counter in the fast forward wind or rewind modes.
Further, the conventional electronic counter is defective in the tape counter precision when the tape is driven by the capstan. This arises from the fact that the ratio with respect to a change of the rotational speed of the reel shaft is small when the amount of tape taken up by the tape reel changes from zero to the maximum. The change ratio is generally 2 to 3 in a cassette type tape recorder. For example, a decimal number of three digits is assumed to be used for digitally displaying the tape running positions. In this case, at least 100 data must be taken out from the change ratio of 2 to 3. Usually, the tape base uses a thin and flexible polyester film. For this, it is very difficult to correctly take out a number of data from such a small change ratio. For example, the outer diameter of the tape when the tape of 30 m is taken up around the tape reel under a slight tension in the fast forward wind is slightly different from that when the same is taken up under a high tension in the playback. In other words, even if the lengths of the tape taken up are the same, the display numerals by the tape counter incorrectly indicate the tape length taken up, or the tape running position, because the rotational speed of the reel shaft can not be defined unconditionally. The incorrectness of the indication is more remarkable as the change ratio is smaller and the display digits are larger.